How much clearance should a transit case leave inside?

About 5 mm per side off the envelope, or 2 mm off the insert outline.

Is a 3 mm side wall enough?

It depends on the rating: 3.0 mm suits 25 kg, while 50 kg wants 4.0 mm, or the wall bulges and the lid stops sealing.

Are rated load and stack height the same figure?

No. Rated load is what one case carries; stack height is a recommendation at a given weight, four high at 15 kg but two at 30 kg.

How should a protection rating be written to avoid disputes?

Both digits, plus test conditions and a pass criterion: dust 6 names the talcum hours, water 5 the spray rate.

Can fork entry height be changed to suit our trucks?

Width can be adapted, height should not, since below 100 mm the forks scrape.

How to Set Transit Case Specifications: Size, Wall and Load

Quick answer: A transit case specification is not three numbers but values that push against each other. Internal size follows the contents, external size the pallet module, wall thickness sets tare and load, and the stacking case rechecks the wall.

Six Inputs Behind a Transit Case Specification
Internal and External Dimensions with Tolerances
Wall Thickness, Tare Weight and Rated Load
How to Write the Sealing and Dust Rating
Stacking Pads, Fork Entry and Marking Zones
FAQ

1. Six Inputs Behind a Transit Case Specification

The usual fault is numbers without measuring points: 600 mm at the rim or at the insert top differs by 20 mm.

Parameter	How to write it	Example
Internal size	Clear space, with datum	600 x 400 x 320 mm
External size	Maximum, latches in	640 x 440 x 360 mm
Wall	Side, base, lid	Side 4.0, base 5.5 mm
Tare	Without insert	4.6 kg
Rated load	Uniform static, timed	50 kg, 24 hours
Protection	Two digits plus tests	Dust 6, water 5

Two inputs often go missing: service temperature and cleaning method.

2. Internal and External Dimensions with Tolerances

Internal size comes from the contents envelope with 5 mm per side: more lets goods shift, less keeps the insert out.

Transit case: a white case open on a bench, black foam cutouts, grey plastic parts, blue racking behind

Tolerances run as two sets: plus or minus 2 mm inside for the insert, 3 mm outside for the pallet slot, plus a 3 mm diagonal limit that exposes moulded distortion.

External size is the maximum outline, latches included; a case that jams in a rack usually has 8 mm of hardware outside the drawing. A 1200 x 800 mm pallet takes four 600 x 400 mm footprints, 620 mm only three.

3. Wall Thickness, Tare Weight and Rated Load

Wall thickness sets weight, stiffness and cooling time at once: 3.0 to 4.0 mm on the side adds about 1.8 kg and a dozen seconds of cycle.

Grade	Wall, side and base	Tare	Rated load	Stacking
Light	3.0 and 4.0 mm	2.8 kg	25 kg	3 high
Standard	4.0 and 5.5 mm	4.6 kg	50 kg	4 high
Heavy	5.5 and 7.0 mm	7.2 kg	80 kg	5 high

Rated load must state static or concentrated and for how long: 24 hours at a safety factor of 3, tested at triple the rating with no set past 2 mm.

Stack height comes back from the bottom case: four high at 15 kg loads 45 kg, inside the 50 kg grade. Polypropylene softens at 60 degrees Celsius, so open-yard stacking rates at seventy percent.

4. How to Write the Sealing and Dust Rating

A rating is two digits, solids then liquids: dust 5 with water 4, dust 6 with water 5, dust 6 with water 7.

Transit case: a beige case open on a shelf, black gasket on the lid edge, wrenches in foam, machines behind

Quoting a rating without test conditions hides the risk: dust 6 is eight hours in a talcum chamber, water 5 is 12.5 litres per minute at 3 metres for 3 minutes, water 7 is immersion at 1 metre for 30 minutes.

Only two features deliver the rating: gasket compression of at least 25 percent and latch spacing no wider than 200 mm. Widen the spacing and the rim lifts between latches.

5. Stacking Pads, Fork Entry and Marking Zones

A lid groove meets a base rib, tight enough to hold, loose enough not to bind in cold.

Interface	Size	Tolerance	Check
Stacking groove	12 x 8 mm	0.5 to 1 mm	Three-high offset stack
Fork entry	200 x 100 mm	Height plus or minus 3 mm	Forks two thirds deep
Marking zone	120 x 80 mm	30 mm below top	Clears parting line

The 100 mm entry covers a 45 mm blade plus clearance; the roof carries the load, so fork cases are checked at 1.25 times the rating.

Marking zones stay clear of the parting line, since a label across it splits. Keep two faces, so a turned transit case still shows one.

Conclusion

A specification is ordered constraints: contents set internal size, the pallet external size, load the wall, and the stacking case checks both.

Tolerances and test conditions are the least visible lines and the first tested. Write the datum, the diagonal and the pass criterion, and a transit case becomes deliverable.

This article discusses only the container (case body) side of specifications and design intent, and does not cover any handling, loading or use of the contents.